Projection position detection device, image projection system, and projection position detection method

ABSTRACT

A projection position detection device includes: a spectroscopic camera receiving light from an image pickup range including a projection image projected onto a projection target, and picking up a plurality of spectral images corresponding to different wavelengths from each other; a spectrum computation unit computing an optical spectrum of each pixel, based on the plurality of spectral images; a feature point detector detecting a feature point in the image pickup range, based on the optical spectrum of the pixel; and a projection position calculator calculating a relative position of the projection image to the feature point.

The present application is based on, and claims priority from, JPApplication Serial Number 2019-013984, filed Jan. 30, 2019, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a projection position detectiondevice, an image projection system, and a projection position detectionmethod.

2. Related Art

According to the related art, there is an image projection systemcontrolling the position or the like of a projection image projected bya projector.

For example, JP-A-2004-341029 describes a system that detects theposition of a screen, using a camera, and controls the position of aprojection image in relation to the screen. This system detects eachcorner of a rectangular screen, based on an image picked up by each oftwo cameras, then calculates the distance from each camera to eachcorner, and thus calculates a relative position of the screen to theprojector. Based on the calculated relative position, the angle, theamount of zoom, and the like of a projection lens are adjusted. Thus, animage fitting a projection area on the screen is projected.

However, in the system described in JP-A-2004-341029, when an image isprojected onto a uniform wall surface or the like instead of the screen,a projection position of the image cannot be set since there is noreference point for detecting the projection position of the image.Therefore, when the projection position of the image is shifted due tovibration at the installation site or a touch by a human or the like, itis difficult to detect this shift.

SUMMARY

A projection position detection device according to an aspect of thepresent disclosure includes: a spectroscopic camera receiving light froman image pickup range including a projection image projected onto aprojection target, and picking up a plurality of spectral imagescorresponding to different wavelengths from each other; a spectrumcomputation unit computing an optical spectrum of each pixel, based onthe plurality of spectral images; a feature point detection unitdetecting a feature point in the image pickup range, based on theoptical spectrum of the pixel; and a projection position calculationunit calculating a relative position of the projection image to thefeature point.

In the projection position detection device, the spectroscopic cameramay include: a variable-wavelength interference filter having a pair ofreflection films facing each other and a gap changing unit changing adimension of a gap between the pair of reflection films; and an imagepickup element picking up an image of light transmitted through thevariable-wavelength interference filter.

In the projection position detection device, the spectroscopic cameramay pick up the spectral image corresponding to a wavelength in anear-infrared range.

The projection position detection device may further include a lightsource casting light including a wavelength in a near-infrared range,onto the projection target.

An image projection system according to another aspect of the presentdisclosure includes: the foregoing projection position detection device;a projection lens projecting the projection image onto the projectiontarget; a lens adjustment mechanism performing optical axis adjustmentor zoom adjustment of the projection lens; and a lens control unitcontrolling the lens adjustment mechanism, based on an amount of changein the relative position of the projection image to the feature point.

An image projection system according to another aspect of the presentdisclosure includes: the foregoing projection position detection device;and an image processing unit correcting the projection image, based onan amount of change in the relative position of the projection image tothe feature point.

A projection position detection method according to another aspect ofthe present disclosure includes: an image pickup step of receiving lightfrom an image pickup range including a projection image projected onto aprojection target, and picking up a plurality of spectral imagescorresponding to different wavelengths from each other; a spectrumcomputation step of computing an optical spectrum of each pixel, basedon the plurality of spectral images; a feature point detection step ofdetecting a feature point in the image pickup range, based on theoptical spectrum of the pixel; and a projection position calculationstep of calculating a relative position of the projection image to thefeature point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an image projection system and aprojection target according to an embodiment of the present disclosure.

FIG. 2 is a block diagram showing a schematic configuration of the imageprojection system according to the embodiment.

FIG. 3 is a block diagram showing a schematic configuration of aprojection position control unit in the embodiment.

FIG. 4 is a schematic view showing a schematic configuration of aspectroscopic camera in the embodiment.

FIG. 5 is a flowchart explaining a flow of initial setting in the imageprojection system according to the embodiment.

FIG. 6 is a schematic view showing an example of an analysis image inthe embodiment.

FIG. 7 is a flowchart explaining an operation of the image projectionsystem according to the embodiment.

FIG. 8 is a schematic view showing an example of an analysis image inthe embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

An embodiment of the present disclosure will now be described withreference to the drawings.

FIG. 1 is a schematic view showing an image projection system 1 and aprojection target 101 according to the embodiment. FIG. 2 is a blockdiagram showing a schematic configuration of the image projection system1.

The image projection system 1 according to the embodiment has aprojector 2 and a spectroscopic camera 3 coupled to the projector 2, asshown in FIG. 1.

The image projection system 1 includes the projection position detectiondevice according to the present disclosure and is configured to controlthe position of a projection image Ip projected on the projection target101 such as a wall surface by the projector 2, based on a spectral imagepicked up by the spectroscopic camera 3.

Configuration of Projector 2

The projector 2 has a display unit 21, a lens adjustment mechanism 22,and a control unit 23, as shown in FIG. 2. Although not illustrated inthe drawing, the projector 2 also has a power-supply device supplyingelectric power to an electronic component forming the projector 2, and acooling device cooling a cooling target, and the like.

The display unit 21 forms and projects an image corresponding to a drivesignal inputted from the control unit 23. The display unit 21 has alight source 211, a liquid crystal panel 212, and a projection lens 213.

The light source 211 illuminates an image forming area on the liquidcrystal panel 212. As the light source 211, a configuration having alight source lamp such as an ultra-high-pressure mercury lamp and areflection mirror reflecting the light emitted from the light sourcelamp into one direction can be employed. Also, a configuration having asolid-state light source such as LED (light-emitting diode) and LD(laser diode) can be employed as an example. The liquid crystal panel212 is a light modulation device driven in response to the drive signaland modulating the light incident thereon from the light source 211.

The projection lens 213 is an optical projection device projecting animage formed at the liquid crystal panel 212 onto a projection targetsurface of a screen, in an enlarged form. As an example of theprojection lens 213, a lens assembly having a lens barrel and aplurality of lenses arranged inside the lens barrel can be employed. Asone of such a plurality of lenses, the projection lens 213 has a zoomlens 213A enlarging/reducing the incident image and projecting theenlarged/reduced image onto the projection target surface. The zoom lens213A moves forward and backward along the optical axis of the projectionlens 213.

The lens adjustment mechanism 22 moves the projection lens 213 along anX-axis orthogonal to the optical axis of the projection lens 213 andalong a Y-axis orthogonal to the optical axis and orthogonal to theX-axis and thus adjusts the projection position. The lens adjustmentmechanism 22 also moves the zoom lens 213A along a Z-axis, which isalong the optical axis of the projection lens 213, and thusenlarges/reduces the projection image.

That is, the lens adjustment mechanism 22 has an X shift unit 221shifting the optical axis of the projection lens 213 along theX-direction, a Y shift unit 222 shifting the optical axis of theprojection lens 213 along the Y-direction, and a zoom unit 223 movingthe zoom lens 213A along the Z-axis.

When the optical axis of the projection lens 213 is shifted to the +Yside, the projection image Ip is moved to the +Y side. Similarly, whenthe optical axis of the projection lens 213 is shifted to the −Y side,the projection image Ip is moved to the −Y side.

When the projection lens 213 is moved to the +X side, the projectionimage Ip is moved to the +X side. Similarly, when the projection lens213 is moved to the −X side, the projection image Ip is moved to the −Xside.

When the zoom lens 213A is moved to one side along the Z-axis by thelens adjustment mechanism 22 and the angle of view is expanded, the sizeof the projection image Ip increases. Meanwhile, when the zoom lens 213Ais moved to the other side along the Z-axis and the angle of view isnarrowed, the size of the projection image Ip decreases.

The lens adjustment mechanism 22 is not particularly limited to anyspecific configuration. However, for example, the lens adjustmentmechanism 22 has an X-axis guide holding the projection lens 213 in sucha way as to be movable along the X-axis, a Y-axis guide holding theprojection lens 213 in such a way as to be movable along the Y-axis, anda Z-axis guide moving the zoom lens 213A along the Z-axis inside theprojection lens 213. Each axis guide is provided with a stepper motorsupplying a driving force to drive the projection lens 213 or the zoomlens 213A. In this example, the lens adjustment mechanism 22 drives thestepper motor corresponding to each axis by a predetermined amount,based on a lens drive signal from the control unit 23, and thus movesthe projection lens 213 or the zoom lens 213A.

The control unit 23 controls the operation of the entirety of theprojector 2 including the display unit 21. The control unit 23 is formedas a circuit board where a CPU (central processing unit), a ROM(read-only memory), and a RAM (random-access memory) or the like aremounted. As the CPU in the control unit 23 executes program stored inthe ROM, the control unit 23 functions as an image processing unit 231,a display control unit 232, a lens control unit 233, and a projectionposition control unit 240. The control unit 23 also includes a storageunit 234 storing an initial position of the projection image Ip or thelike.

The image processing unit 231 processes image data (including an imagesignal) received from outside and draws an image for one screen into aframe memory, not illustrated, based on the image data.

The display control unit 232 reads out an image drawn by the imageprocessing unit 231 according to need and sequentially drives the liquidcrystal panel 212 to form the image.

The lens control unit 233 controls the operation of the lens adjustmentmechanism 22.

The storage unit 234 stores an initial setting of the projection imageIp or the like, described later.

The projection position control unit 240 analyzes a spectral imagepicked up by the spectroscopic camera 3 and outputs a correctioninstruction to the lens control unit 233 or the image processing unit231, based on the result of the analysis. Thus, the projection positioncontrol unit 240 controls the projection position of the projectionimage Ip at the projection target 101, or the like. The projectionposition control unit 240, along with the spectroscopic camera 3, formsa projection position detection device 100. The projection positioncontrol unit 240 includes a spectrum computation unit 241, a featurepoint detection unit 242, a projection position calculation unit 243,and a correction instruction unit 244, as shown in FIG. 3.

Configuration of Spectroscopic Camera 3

The spectroscopic camera 3 includes a near-infrared light source 31, anincident optical system 32, a variable-wavelength interference filter33, an image pickup element 34, and a camera control unit 35, as shownin FIG. 2.

The near-infrared light source 31 is a light source castingnear-infrared light to an image pickup range of the spectroscopic camera3.

FIG. 4 is a schematic view showing the configuration of each of theincident optical system 32, the variable-wavelength interference filter33, and the image pickup element 34.

The incident optical system 32 is formed of, for example, a telecentricoptical system or the like and guides incident light to thevariable-wavelength interference filter 33 and the image pickup element34 in such a way that the optical axis and a main beam become parallelor substantially parallel to each other.

The variable-wavelength interference filter 33 is a Fabry-Perot etalonfilter and has a pair of reflection films 331, 332 facing each other andan electrostatic actuator 333 (the gap changing unit according to thepresent disclosure) that can change the distance between the reflectionfilms 331, 332. As the voltage applied to the electrostatic actuator 333is controlled, the variable-wavelength interference filter 33 can changethe wavelength (spectral wavelength) of light transmitted through thereflection films 331, 332.

The image pickup element 34 is formed of, for example, an image sensorsuch as a CCD (charge-coupled device) or CMOS (complementary metal-oxidesemiconductor) and picks up an image of image light transmitted throughthe variable-wavelength interference filter 33. In the spectroscopiccamera 3 in this embodiment, the light transmitted through thevariable-wavelength interference filter 33 becomes incident on eachpixel of the image pickup element 34.

The camera control unit 35 is an integrated circuit including a CPU(central processing unit) and a built-in memory or the like. As the CPUin the camera control unit 35 reads out and executes a computer programrecorded in the built-in memory, the camera control unit 35 functions asa wavelength switching unit 351 and an image pickup control unit 352.The camera control unit 35 also includes a storage unit 353.

In the storage unit 353, a drive table showing a correspondence betweena wavelength of light transmitted through the variable-wavelengthinterference filter 33 and a command value to the electrostatic actuator333 is recorded.

The wavelength switching unit 351 changes the command value inputted tothe electrostatic actuator 333 of the variable-wavelength interferencefilter 33, based on the drive table.

The image pickup control unit 352 acquires a received light signal(spectrum information) outputted from each pixel of the image pickupelement 34 and thus obtains a spectral image.

The spectroscopic camera 3 is configured to be able to transmit theacquired spectral image to the projector 2. Specifically, thespectroscopic camera 3 may be wirelessly coupled to the projector 2,using radio waves, infrared light or the like, or may be wired to theprojector 2 via a cable line or the like.

Initial Setting of Image Projection System 1

Initial setting of the image projection system 1 will now be describedwith reference to the flowchart of FIG. 5. The initial setting of theimage projection system 1 uses a projection position detection methodaccording to this embodiment. In the description below, it is assumedthat the projector 2 projects an image of a permanent exhibition andthat the projection target 101 is a uniformly colored planar wallsurface.

First, the projector 2 and the spectroscopic camera 3 are installedrespectively (step S11).

Specifically, for example, the user installs the projector 2 in such away that the projection image Ip is displayed in a desired size at adesired position, while checking the projection image Ip projected onthe projection target 101. Also, for example, the user installs thespectroscopic camera 3 in such a way that a predetermined rangeincluding the projection image Ip projected on the projection target 101becomes an image pickup range.

Here, it is assumed that the image pickup range of the spectroscopiccamera 3 includes not only the projection image Ip but also a marker M.The marker M in this embodiment is a rectangular plate (facilityinformation board or the like) placed at a wall surface that is theprojection target 101, as shown in FIG. 1. However, this is notlimiting. The marker M may be an unevenness in painting, a stain, ascratch or the like appearing on the wall surface that is the projectiontarget 101.

Subsequently, the projector 2 starts projecting the projection image Ip(step S12). The projector 2 may continue projecting the projection imageIp from step S11.

Next, the spectroscopic camera 3 picks up a plurality of spectral imagescorresponding to different wavelengths from each other (step S13; imagepickup step).

At this time, the near-infrared light source 31 casts near-infraredlight of 750 nm to 950 nm onto the image pickup range of thespectroscopic camera 3.

The wavelength switching unit 351 sequentially reads out command valuesfrom the drive table and inputs the command values in order into theelectrostatic actuator 333 of the variable-wavelength interferencefilter 33. Thus, the transmission wavelength of the variable-wavelengthinterference filter 33 is sequentially changed to a plurality of presetwavelengths (target wavelengths). The target wavelengths are set every20 nm within a range from visible light to near-infrared light (forexample, 680 nm to 880 nm).

The image pickup element 34 is controlled by the image pickup controlunit 352 and thus performs image pickup every time the transmissionwavelength of the variable-wavelength interference filter 33 is set to atarget wavelength. Thus, a spectral image corresponding to each targetwavelength is picked up.

Next, the spectrum computation unit 241 acquires the plurality ofspectral images from the spectroscopic camera 3 and computes the opticalspectrum of each pixel, based on the plurality of spectral images (stepS14; spectrum computation step). Thus, an analysis image Ia as shown inFIG. 6 is generated.

The analysis image Ia is segmented into a plurality of pixel areas,based on the optical spectrum of each pixel.

The projection image Ip is an image projected with visible light andtherefore has the highest reflection intensity around a wavelength of680 nm. Therefore, a pixel area having a maximum intensity around awavelength of 680 nm is defined as a projection image area R1.

A pixel area showing a different optical spectrum from the opticalspectrum of the projection image area R1, in the periphery of theprojection image area R1, is defined as a background area R2.

A pixel area surrounded by the background area R2 and showing adifferent optical spectrum from that of the projection image area R1 andthe background area R2 is defined as a marker area R3.

The feature point detection unit 242 detects a boundary line of themarker area R3 in the analysis image Ia and derives corners Cm1 to Cm4of the boundary line. The feature point detection unit 242 then detectsthe centroid with respect to the four corner points Cm1 to Cm4, as afeature point G (step S15; feature point detection step).

Next, the projection position calculation unit 243 detects a boundaryline of the projection image area R1 in the analysis image Ia andderives corners Cp1 to Cp4 of the boundary line. Then, as the relativeposition of the projection image Ip to the feature point G, theprojection position calculation unit 243 calculates coordinates(Xa1,Ya1) to (Xa4,Ya4) of the corners Cp1 to Cp4, with the feature pointG defined as the origin (step S16; projection position calculationstep).

Subsequently, the projection position calculation unit 243 stores thecoordinates (Xa1,Ya1) to (Xa4,Ya4) calculated at step S16 into thestorage unit 234, as an initial position of the projection image Ip(step S17).

The initial setting of the image projection system 1 thus ends.

Operation of Image Projection System 1

The operation of the image projection system 1 will now be describedwith reference to the flowchart of FIG. 7. The flowchart of FIG. 7 isstarted as the projector 2 starts projecting the projection image Ip.

First, the spectroscopic camera 3 determines whether the current time isa position detection timing or not (step S21). When the result of thedetermination is Yes, the processing goes to step S22. When the resultof the determination is No, the processing waits until it is Yes. Theposition detection is set, for example, every predetermined time period.

Next, the spectroscopic camera 3 picks up a plurality of spectral imagescorresponding to different wavelengths from each other (step S22). Basedon the plurality of spectral images that are picked up, the projectionposition control unit 240 calculates the relative position of theprojection image Ip to the feature point G, that is, coordinates(Xb1,Yb1) to (Xb4,Yb4) of the corners Cp1 to Cp4 with the feature pointG defined as the origin (step S23).

Step S22 is similar to the foregoing step S13. Step S23 is similar tothe foregoing steps S14 to S16.

Next, the correction instruction unit 244 compares the coordinates(Xb1,Yb1) to (Xb4,Yb4) calculated in step S23 with the initial position(Xa1,Ya1) to (Xa4,Ya4) stored in the storage unit 234 and calculatesamounts of change (ΔX1,ΔY1) to (ΔX4,ΔY4) from the initial position (stepS24).

Next, the correction instruction unit 244 determines whether the amountsof change (ΔX1,ΔY1) to (ΔX4,ΔY4) calculated in step S24 are equal to orlower than a preset threshold in terms of each of the X coordinate andthe Y coordinate, or not (step S25).

When it is determined that the amounts of change (ΔX1,ΔY1) to (ΔX4,ΔY4)are equal to or lower than the threshold in terms of both the Xcoordinate and the Y coordinate (Yes in step S25), the processingreturns to step S21.

Meanwhile, when it is determined that the amounts of change (ΔX1,ΔY1) to(ΔX4,ΔY4) are not equal to or lower than the threshold in terms of atleast one of the X coordinate and the Y coordinate (No in step S25), theprocessing goes to step S26.

Next, the correction instruction unit 244 determines whether there is ashift from the initial state in terms of the position, size or shape ofthe projection image Ip, based on the amounts of change (ΔX1,ΔY1) to(ΔX4,ΔY4), and outputs a correction instruction to the lens control unit233 or the image processing unit 231, based on the result of thedetermination (step S26).

For example, FIG. 8 shows an analysis image Ia in the case where theprojection image Ip is shifted along the Y-axis and the X-axis from theinitial position. In FIG. 8, the projection image area R1 at the initialposition is indicated by a dashed line, and the current projection imagearea R1 is indicated by a solid line.

In the example shown in FIG. 8, the amounts of change ΔX1 to ΔX4 arevalues equal to each other (ΔX in FIG. 8), and the amounts of change ΔY1to ΔY4 are values equal to each other (ΔY in FIG. 8). In such a case,the correction instruction unit 244 determines that the projection imageIp is shifted in position, and outputs a correction instruction based onthe amount of change (ΔX,ΔY), to the lens control unit 233. The lenscontrol unit 233, to which this correction instruction is inputted,controls the X shift unit 221, based on the amount of change ΔX, andcontrols the Y shift unit 222, based on the amount of change ΔY. Thus,the X shift unit 221 and the Y shift unit 222 moves the projection lens213 along the X-axis and the Y-axis in such a way that the position ofthe projection image Ip becomes closer to the initial position. That is,the projection image Ip is controlled in such a way as to maintain apredetermined projection position.

When it is determined that the projection image Ip is changed in size,the correction instruction unit 244 outputs a correction instructionbased on the amounts of change (ΔX1,ΔY1) to (ΔX4,ΔY4), to the lenscontrol unit 233. The lens control unit 233 controls the zoom unit 223,based on the correction instruction, and thus makes the size of theprojection image Ip closer to the initial state.

When it is determined that the projection image Ip is changed in shape,the correction instruction unit 244 outputs a correction instructionbased on the amounts of change (ΔX1,ΔY1) to (ΔX4,ΔY4), to the imageprocessing unit 231. The image processing unit 231 corrects the data ofthe projection image Ip, based on the correction instruction, and thusmakes the shape of the projection image Ip closer to the initial state.

When the projection is ended as the power of the projector 2 is turnedoff or the like (Yes in step S27), this flow ends. Meanwhile, whenprojection continues (No in step S27), the processing returns to stepS21 and the flow is repeated.

Effects of this Embodiment

The projection position detection device 100 and the image projectionsystem 1 according to the foregoing embodiment can achieve the followingeffects.

(1) The projection position detection device 100 according to theembodiment includes: the spectroscopic camera 3 receiving light from animage pickup range including the projection image Ip projected onto theprojection target 101, and picking up a plurality of spectral imagescorresponding to different wavelengths from each other; the spectrumcomputation unit 241 computing an optical spectrum of each pixel, basedon the plurality of spectral images; the feature point detection unit242 detecting the feature point G in the image pickup range, based onthe optical spectrum of the pixel; and the projection positioncalculation unit 243 calculating a relative position of the projectionimage Ip to the feature point G.

According to such a configuration, the feature point G detected in theimage pickup range of the spectroscopic camera 3 serves as a referencepoint for calculating the projection position of the projection imageIp. Therefore, the projection position of the projection image Ip can beset regardless of the type of the projection target 101. Thus, when theprojection position of the projection image Ip is shifted due tovibration at the installation site or a touch by a human or the like,this shift can be easily detected.

(2) In the embodiment, projection position detection device, thespectroscopic camera 3 includes: the variable-wavelength interferencefilter 33 having the pair of reflection films 331, 332 facing each otherand the electrostatic actuator 333 changing the dimension of the gapbetween the pair of reflection films 331, 332; and the image pickupelement 34 picking up an image of light transmitted through thevariable-wavelength interference filter 33.

In such a configuration, light of a plurality of wavelengths is receivedat the same pixel of the image pickup element 34. Therefore, the featurepoint Gin the image pickup range can be detected with high accuracy andhigh resolution.

(3) In the embodiment, the spectroscopic camera 3 picks up a spectralimage corresponding to a wavelength in a near-infrared range.

The related-art system described JP-A-2004-341029 uses a general camera.Therefore, a picked-up image picked up in a dark space is obscure and itis difficult to detect the corners of the screen, based on such apicked-up image. That is, it is difficult to detect the projectionposition of the projection image in a dark space.

In contrast, in the embodiment, a spectral image corresponding to awavelength in a near-infrared range is picked up, and the projectionposition of the projection image Ip is detected, based on this spectralimage. The wavelength in the near-infrared range can make visible thedifference in light reflectivity due to the composition of the targetobject. Therefore, the projection position of the projection image Ipcan be properly detected even in a dark space.

(4) The spectroscopic camera 3 in the embodiment further includes thenear-infrared light source 31 casting light including a wavelength in anear-infrared range, onto the projection target 101.

According to such a configuration, the projection position of theprojection image Ip can be more properly detected even in a dark space,as described above. Also, the light of a wavelength in the near-infraredrange is invisible to human eyes and therefore does not change the colortone of the projection image Ip. Moreover, this light enables theprojection image Ip to appear sharply, without decreasing thebright/dark contrast by illumination.

(5) The image projection system 1 in the embodiment includes: theforegoing projection position detection device 100; the projection lens213 projecting the projection image Ip onto the projection target 101;the lens adjustment mechanism 22 performing optical axis adjustment orzoom adjustment of the projection lens 213; and the lens control unit233 controlling the lens adjustment mechanism 22, based on the amount ofchange in the relative position of the projection image Ip to thefeature point G.

According to such a configuration, the projection image Ip can becontrolled to be at a predetermined position or in a predetermined size.

(6) The image projection system 1 in the embodiment includes: theforegoing projection position detection device 100; and the imageprocessing unit 231 correcting the projection image Ip, based on theamount of change in the relative position of the projection image Ip tothe feature point G.

According to such a configuration, the projection image Ip can becontrolled to be in a predetermined shape.

As a related art, there is a technique of projecting a pattern imageonto a projection target, then picking up the pattern image, and thuscorrecting a parameter of a projection image. JP-A-2008-287426 is anexample of this technique. However, in such a related-art technique, theoriginal projection of the projection image must be interrupted in orderto project the pattern image.

In contrast, in the embodiment, the projection position of theprojection image Ip can be controlled without interrupting theprojection of the projection image Ip.

MODIFICATION EXAMPLES

The present disclosure is not limited to the foregoing embodiment andincludes modifications, improvements and the like within a range thatcan achieve the object of the present disclosure.

Modification Example 1

In the embodiment, the centroid with respect to the corners Cm1 to Cm4of the marker area R3 is detected as the feature point G. However, thisis not limiting.

For example, each of the corners Cm1 to Cm4 of the marker area R3 may bedetected as a feature point, and the relative position of the cornersCp1 to Cp4 of the projection image area R1 to these feature points maybe calculated respectively.

Alternatively, one of the detected corners Cm1 to Cm4 of the marker areaR3 may be detected as a feature point.

Modification Example 2

In the embodiment, a rectangular plate is detected as the marker M.However, this is not limiting.

For example, the marker M may be an unevenness in painting, a stain, ascratch or the like appearing on the wall surface that is the projectiontarget 101. In such a case, a general image processing technique can beused to detect a feature point. As an example of this, the center of aninscribed circle or a circumscribed circle at an edge forming a stainmay be detected as a feature point.

Modification Example 3

In the embodiment, the coordinates of the four corners Cp1 to Cp4 of theprojection image area R1 are calculated as the projection position ofthe projection image Ip. However, this is not limiting.

For example, when a large shift is not assumed, the coordinates of atleast one of the four corners Cp1 to Cp4 of the projection image area R1may be calculated.

Also, the centroid with respect to the corners Cp1 to Cp4 of theprojection image area R1 may be used as the projection position of theprojection image Ip.

Alternatively, an arbitrary point on the boundary line of the projectionimage area R1 may be used as the projection position of the projectionimage Ip.

Modification Example 4

In the embodiment, the spectroscopic camera 3 picks up a spectral imagecorresponding to a wavelength in a near-infrared range. However, thespectroscopic camera 3 may pickup a spectral image corresponding to awavelength in an ultraviolet range. The spectroscopic camera 3 may alsohave a light source casting light including a wavelength in anultraviolet range onto the projection target 101. Similarly tonear-infrared light, ultraviolet light is invisible to human eyes andtherefore does not change the color tone of the projection image Ip.

Modification Example 5

In the embodiment, the lens adjustment mechanism 22 controls theposition and size of the projection image Ip, and the image processingunit 231 controls the shape of the projection image Ip. However, this isnot limiting. For example, when the projection image Ip is an imageprojected in a smaller area than the projectable range of the projector2, the image processing unit 231 may control the position and size ofthe projection image Ip.

Modification Example 6

In the embodiment, the spectroscopic camera 3 has thevariable-wavelength interference filter 33. However, the spectroscopiccamera 3 may have another spectral filter.

Modification Example 7

In the embodiment, the projector 2 and the spectroscopic camera 3 areformed separately from each other. However, these may be unifiedtogether.

What is claimed is:
 1. A projection position detection devicecomprising: a spectroscopic camera configured to receive light from aprojection target, the projection target having a background, a marker,and a projected image area, a projected image being projected on theprojected image area, the spectroscopic camera being configured tocapture a plurality of spectral images corresponding to differentwavelengths from each other of the projection target based on thereceived light, optical spectrums of the background, the marker, and theprojected image on the projected image area of the projection targetbeing different from each other; a memory configured to store a program;and a processor configured to execute the program so as to: cause thespectroscopic camera to capture the plurality of spectral images of theprojection target; obtain the optical spectrums of every pixel of thecaptured plurality of spectral images; determine a position of themarker on the projection target based on the obtained optical spectrums;determine an area of the projected image on the projection target basedon the obtained optical spectrums; and determine a relative positionbetween the marker and the projected image.
 2. The projection positiondetection device according to claim 1, wherein the spectroscopic cameraincludes: a variable-wavelength interference filter having a pair ofreflection films facing each other and a gap changing unit that isconfigured to change a dimension of a gap between the pair of reflectionfilms; and an image pickup element configured to capture the pluralityof spectral images corresponding to the light transmitted through thevariable-wavelength interference filter.
 3. The projection positiondetection device according to claim 1, wherein each of the plurality ofspectral images corresponds to a wavelength in a near-infrared range. 4.The projection position detection device according to claim 3, furthercomprising a light source configured to emit light including thewavelength in the near-infrared range onto the projection target.
 5. Animage projection system comprising: a projection position detectiondevice, the projection position detection device including: aspectroscopic camera configured to receive light from a projectiontarget, the projection target having a background, a marker, and aprojected image area, a projected image being projected on the projectedimage area, the spectroscopic camera being configured to capture aplurality of spectral images corresponding to different wavelengths fromeach other of the projection target based on the received light, opticalspectrums of the background, the marker, and the projected image on theprojected image area of the projection target being different from eachother; a memory configured to store a program; and a processorconfigured to execute the program so as to: cause the spectroscopiccamera to capture the plurality of spectral images of the projectiontarget; obtain the optical spectrums of every pixel of the capturedplurality of spectral images; determine a position of the marker on theprojection target based on the obtained optical spectrums; determine anarea of the projected image on the projection target based on theobtained optical spectrums; and determine a relative position betweenthe marker and the projected image; a projection lens configured toproject the projection image onto the projection target; a lensadjustment mechanism configured to perform optical axis adjustment orzoom adjustment of the projection lens; and a lens controller configuredto control the lens adjustment mechanism based on an amount of change inthe relative position of the projection image to the feature point. 6.The image projection system according to claim 5, further comprising: animage processor configured to correct the projection image based on anamount of change in the relative position of the projection image to thefeature point.
 7. A projection position detection method for causing aprocessor to execute a program stored in a memory, the method comprisingexecuting on the processor the steps of: receiving light from aprojection target, the projection target having a background, a marker,and a projected image area, a projected image being projected on theprojected image area; capturing a plurality of spectral imagescorresponding to different wavelengths from each other of the projectiontarget based on the received light, optical spectrums of the background,the marker, and the projected image on the projected image area of theprojection target being different from each other; obtaining the opticalspectrums of every pixel of the captured plurality of spectral images;determining a position of the marker on the projection target based onthe obtained optical spectrums; determining an area of the projectedimage on the projection target based on the obtained optical spectrums;and determining a relative position between the marker and the projectedimage.